A. Field of the Invention
The present invention relates to a clinching type stapler and, more particularly, to a stapler having an anvil structure for clinching staples that is not only economically fabricated and easily adjusted, but is also compact and integrally formed to permit stapling in closed or confined areas.
B. Description of the Background Art
There are a number of applications in which staplers are most efficiently used to join material by diverging the legs of a stable that is driven to provide an outwardly clinched staple. U.S. Pat. Nos. 2,420,258 and 3,417,908 disclose outwardly of clinching staplers in which an anvil normally disposed beneath the legs of a staple engages these legs of the staple as driven to impart an outwardly directed curl or clinch to the legs. These anvils are formed of resilient material and are deflected or cammed out of a staple raceway or drive track by engagement with a driver blade or the crown of the staple, thereby permitting the discharge of the driven staple. In other outwardly clinching staplers such as that shown in U.S. Pat. No. 3,807,619, the anvil structure is a pivotally mounted, rigid member engaged by a biasing spring and movable into and out of an effective position as the driver blade is reciprocated within the drive track.
These staplers provide effective clinching, but the degree of curl or clinch achieved is directly dependent on forming the staple legs as they engage the anvil and are forced between the anvil surfaces and the adjacent surfaces of a nosepiece defining the drive track. This metal-to-metal engagement results in wear on the engaged anvil surfaces and the nosepiece structures with the result that the degree of curl or clinch attained changes after a number of staples have been driven. In applications in which large numbers of staples are driven daily, the effective life of the tool is frequently less than would be desired. In addition, the springs used with the rigid anvil structure have a shorter useful life than would be desired.
The anvil-nosepiece spacing necessary for proper clinching can be restored by adjusting the relative positions of the anvil-nosepiece structures as wear occurs. U.S. Pat. No. 2,237,438 discloses a clinching stapler in which a screw interposed between a stapler housing and a movable rigid anvil support permits adjustment of a rigid anvil relative to a nosepiece. U.S. Pat. No. 3,152,335 discloses a cam arrangement for controlling the gap between a rigid anvil and a nosepiece structure in an outward clinch stapler. However, both of these arrangements are somewhat difficult to adjust quickly under the time constraints of a high production operation. In addition, one of these units requires so much space that the use of the stapler in confined areas is substantially restricted.